7.6. Exercise: Bang-Bang Control

Question 1

Why does a bang-bang controller often cause the process variable, such as temperature, to oscillate above and below the setpoint?

Solution

A bang-bang controller only reacts after the setpoint or threshold is crossed.

By the time the actuator is switched off, the system may still have inertia, such as thermal or mechanical inertia. This carries the process variable past the setpoint.

When the actuator is off, the system drifts back the other way until the lower threshold is crossed again. This repeated switching creates continuous oscillation.

Question 2

An oven uses bang-bang control to maintain \(180\,^\circ\text{C}\).

Describe what happens if the oven has a large thermal mass compared with if it has a small thermal mass.

Solution

Solution is locked

Question 3

A water tank is kept between \(30\%\) and \(80\%\) full using double-setpoint control of a pump.

Why are two thresholds used instead of a single setpoint?

Solution

Solution is locked